1. Field of the Invention
The invention relates to a polishing pad which is useful for planarizing by polishing a substrate such as a semiconductor device or wafer, and in particular, to a polishing pad having an adhesive for adhering and securing the polishing pad to a platen or other mounting surface.
2. Background of the Invention
Semiconductor wafers having integrated circuits fabricated thereon must be polished to smooth and flat wafer surfaces that in some cases are permitted to vary from a given plane by as little as a fraction of a micron. Such polishing is usually accomplished in a chemical-mechanical polishing (CMP) operation, which utilizes a chemically active slurry that is buffed against the wafer surface by a polishing pad.
A polishing pad is a relatively thin, planar, disk-shaped article. As an example, a DPM (disk pad Mylar(copyright)) polishing pad that is commercially available from Rodel, Inc., of Newark, Del., has a thickness of about 0.0225 inch and a diameter of about 52 inches. Such a pad is not completely rigid across their diameter, that is, the pads are somewhat floppy to conform flatly against a mounting surface, such as that provided by a platen of a known polishing apparatus or machine.
The polishing pad must be placed on a platen of a polishing machine, or on another mounting surface, and secured to the platen or other mounting surface by a pressure sensitive adhesive (PSA) on the back side of the polishing pad. As the polishing pad is placed on the platen or other mounting surface, bubbles of air tend to get trapped between the adhesive and the platen or other mounting surface. Any trapped air will distend the relatively thin pad, thereby causing raised areas or bulges in the polishing surface of the polishing pad. The presence of trapped air prevents the air entrapping portion of the adhesive from contacting and adhering to the platen or other mounting surface. These bulges cannot be eliminated by forcing the air bubbles out from under the pad with a roller. Instead, the bulges must be manually pierced with a hand tool in order to let the trapped air escape, and then the pad can be pressed flat against the platen or other mounting surface to obtain the flattest possible polishing surface. This process is time-consuming, and some small bulges that are undetected cause bulges to remain in the polishing surface. Any bulges in the polishing surface will generate non-uniformities on the polished surface of the wafer workpiece during polishing, thereby causing defects in the polished surface of the wafer. There is a need for a polishing pad which overcomes these problems. There is a further need for a process of manufacturing a polishing pad that overcomes these problems.
According to the invention, a polishing pad comprises a polishing layer and a bottom adhesive layer below the polishing layer. The adhesive layer has an adhesive bottom surface and a hollow air transmitting pathway, for example, a channel, in the adhesive layer extending to an end of the adhesive layer. When the adhesive bottom surface is applied to a platen or other mounting surface, air which is trapped between the adhesive layer and the platen can escape through the channel.
According to one embodiment, the channel comprises an array of intersecting channel segments or grooves. The grooves may be embossed, screen-printed, or otherwise cut in the adhesive bottom surface.
According to another embodiment, a material strand is disposed in a hollow in the adhesive layer, and the channel comprises a portion of the hollow that is unoccupied by the material strand.